diff --git a/libc/system_properties/system_properties.cpp b/libc/system_properties/system_properties.cpp
new file mode 100644
index 0000000..5d13404
--- /dev/null
+++ b/libc/system_properties/system_properties.cpp
@@ -0,0 +1,656 @@
+/*
+ * Copyright (C) 2008 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <errno.h>
+#include <fcntl.h>
+#include <netinet/in.h>
+#include <poll.h>
+#include <stdatomic.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/select.h>
+#include <sys/socket.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <sys/uio.h>
+#include <sys/un.h>
+#include <unistd.h>
+
+#define _REALLY_INCLUDE_SYS__SYSTEM_PROPERTIES_H_
+#include <sys/_system_properties.h>
+#include <sys/system_properties.h>
+
+#include <async_safe/log.h>
+
+#include "private/ErrnoRestorer.h"
+#include "private/bionic_defs.h"
+#include "private/bionic_futex.h"
+#include "private/bionic_macros.h"
+#include "private/bionic_sdk_version.h"
+
+#include "context_node.h"
+#include "contexts.h"
+#include "contexts_pre_split.h"
+#include "contexts_split.h"
+#include "prop_area.h"
+#include "prop_info.h"
+#include "system_property_globals.h"
+
+// We don't want to use new or malloc in properties (b/31659220), and since these classes are
+// small enough and don't have non-trivial constructors, it's easier to just statically declare
+// them than anything else.
+static ContextsSplit contexts_split;
+static ContextsPreSplit contexts_pre_split;
+static Contexts* contexts = nullptr;
+
+#define SERIAL_DIRTY(serial) ((serial)&1)
+#define SERIAL_VALUE_LEN(serial) ((serial) >> 24)
+
+static const char property_service_socket[] = "/dev/socket/" PROP_SERVICE_NAME;
+static const char* kServiceVersionPropertyName = "ro.property_service.version";
+
+// This is public because it was exposed in the NDK. As of 2017-01, ~60 apps reference this symbol.
+__BIONIC_WEAK_VARIABLE_FOR_NATIVE_BRIDGE
+prop_area* __system_property_area__ = nullptr;
+
+char property_filename[PROP_FILENAME_MAX] = PROP_FILENAME;
+size_t pa_size;
+
+class PropertyServiceConnection {
+ public:
+  PropertyServiceConnection() : last_error_(0) {
+    socket_ = ::socket(AF_LOCAL, SOCK_STREAM | SOCK_CLOEXEC, 0);
+    if (socket_ == -1) {
+      last_error_ = errno;
+      return;
+    }
+
+    const size_t namelen = strlen(property_service_socket);
+    sockaddr_un addr;
+    memset(&addr, 0, sizeof(addr));
+    strlcpy(addr.sun_path, property_service_socket, sizeof(addr.sun_path));
+    addr.sun_family = AF_LOCAL;
+    socklen_t alen = namelen + offsetof(sockaddr_un, sun_path) + 1;
+
+    if (TEMP_FAILURE_RETRY(connect(socket_, reinterpret_cast<sockaddr*>(&addr), alen)) == -1) {
+      last_error_ = errno;
+      close(socket_);
+      socket_ = -1;
+    }
+  }
+
+  bool IsValid() {
+    return socket_ != -1;
+  }
+
+  int GetLastError() {
+    return last_error_;
+  }
+
+  bool RecvInt32(int32_t* value) {
+    int result = TEMP_FAILURE_RETRY(recv(socket_, value, sizeof(*value), MSG_WAITALL));
+    return CheckSendRecvResult(result, sizeof(*value));
+  }
+
+  int socket() {
+    return socket_;
+  }
+
+  ~PropertyServiceConnection() {
+    if (socket_ != -1) {
+      close(socket_);
+    }
+  }
+
+ private:
+  bool CheckSendRecvResult(int result, int expected_len) {
+    if (result == -1) {
+      last_error_ = errno;
+    } else if (result != expected_len) {
+      last_error_ = -1;
+    } else {
+      last_error_ = 0;
+    }
+
+    return last_error_ == 0;
+  }
+
+  int socket_;
+  int last_error_;
+
+  friend class SocketWriter;
+};
+
+class SocketWriter {
+ public:
+  explicit SocketWriter(PropertyServiceConnection* connection)
+      : connection_(connection), iov_index_(0), uint_buf_index_(0) {
+  }
+
+  SocketWriter& WriteUint32(uint32_t value) {
+    CHECK(uint_buf_index_ < kUintBufSize);
+    CHECK(iov_index_ < kIovSize);
+    uint32_t* ptr = uint_buf_ + uint_buf_index_;
+    uint_buf_[uint_buf_index_++] = value;
+    iov_[iov_index_].iov_base = ptr;
+    iov_[iov_index_].iov_len = sizeof(*ptr);
+    ++iov_index_;
+    return *this;
+  }
+
+  SocketWriter& WriteString(const char* value) {
+    uint32_t valuelen = strlen(value);
+    WriteUint32(valuelen);
+    if (valuelen == 0) {
+      return *this;
+    }
+
+    CHECK(iov_index_ < kIovSize);
+    iov_[iov_index_].iov_base = const_cast<char*>(value);
+    iov_[iov_index_].iov_len = valuelen;
+    ++iov_index_;
+
+    return *this;
+  }
+
+  bool Send() {
+    if (!connection_->IsValid()) {
+      return false;
+    }
+
+    if (writev(connection_->socket(), iov_, iov_index_) == -1) {
+      connection_->last_error_ = errno;
+      return false;
+    }
+
+    iov_index_ = uint_buf_index_ = 0;
+    return true;
+  }
+
+ private:
+  static constexpr size_t kUintBufSize = 8;
+  static constexpr size_t kIovSize = 8;
+
+  PropertyServiceConnection* connection_;
+  iovec iov_[kIovSize];
+  size_t iov_index_;
+  uint32_t uint_buf_[kUintBufSize];
+  size_t uint_buf_index_;
+
+  DISALLOW_IMPLICIT_CONSTRUCTORS(SocketWriter);
+};
+
+struct prop_msg {
+  unsigned cmd;
+  char name[PROP_NAME_MAX];
+  char value[PROP_VALUE_MAX];
+};
+
+static int send_prop_msg(const prop_msg* msg) {
+  PropertyServiceConnection connection;
+  if (!connection.IsValid()) {
+    return connection.GetLastError();
+  }
+
+  int result = -1;
+  int s = connection.socket();
+
+  const int num_bytes = TEMP_FAILURE_RETRY(send(s, msg, sizeof(prop_msg), 0));
+  if (num_bytes == sizeof(prop_msg)) {
+    // We successfully wrote to the property server but now we
+    // wait for the property server to finish its work.  It
+    // acknowledges its completion by closing the socket so we
+    // poll here (on nothing), waiting for the socket to close.
+    // If you 'adb shell setprop foo bar' you'll see the POLLHUP
+    // once the socket closes.  Out of paranoia we cap our poll
+    // at 250 ms.
+    pollfd pollfds[1];
+    pollfds[0].fd = s;
+    pollfds[0].events = 0;
+    const int poll_result = TEMP_FAILURE_RETRY(poll(pollfds, 1, 250 /* ms */));
+    if (poll_result == 1 && (pollfds[0].revents & POLLHUP) != 0) {
+      result = 0;
+    } else {
+      // Ignore the timeout and treat it like a success anyway.
+      // The init process is single-threaded and its property
+      // service is sometimes slow to respond (perhaps it's off
+      // starting a child process or something) and thus this
+      // times out and the caller thinks it failed, even though
+      // it's still getting around to it.  So we fake it here,
+      // mostly for ctl.* properties, but we do try and wait 250
+      // ms so callers who do read-after-write can reliably see
+      // what they've written.  Most of the time.
+      // TODO: fix the system properties design.
+      async_safe_format_log(ANDROID_LOG_WARN, "libc",
+                            "Property service has timed out while trying to set \"%s\" to \"%s\"",
+                            msg->name, msg->value);
+      result = 0;
+    }
+  }
+
+  return result;
+}
+
+static bool is_dir(const char* pathname) {
+  struct stat info;
+  if (stat(pathname, &info) == -1) {
+    return false;
+  }
+  return S_ISDIR(info.st_mode);
+}
+
+__BIONIC_WEAK_FOR_NATIVE_BRIDGE
+int __system_properties_init() {
+  // This is called from __libc_init_common, and should leave errno at 0 (http://b/37248982).
+  ErrnoRestorer errno_restorer;
+
+  if (contexts != nullptr) {
+    contexts->ResetAccess();
+    return 0;
+  }
+  contexts = nullptr;
+  if (is_dir(property_filename)) {
+    if (!contexts_split.Initialize(false)) {
+      return -1;
+    }
+    contexts = &contexts_split;
+  } else {
+    if (!contexts_pre_split.Initialize(false)) {
+      return -1;
+    }
+    contexts = &contexts_pre_split;
+  }
+  return 0;
+}
+
+__BIONIC_WEAK_FOR_NATIVE_BRIDGE
+int __system_property_set_filename(const char* filename) {
+  size_t len = strlen(filename);
+  if (len >= sizeof(property_filename)) return -1;
+
+  strcpy(property_filename, filename);
+  return 0;
+}
+
+__BIONIC_WEAK_FOR_NATIVE_BRIDGE
+int __system_property_area_init() {
+  if (contexts != nullptr) {
+    contexts->FreeAndUnmap();
+  }
+  // We set this unconditionally as we want tests to continue on regardless of if this failed
+  // and property_service will abort on an error condition, so no harm done.
+  contexts = &contexts_split;
+  if (!contexts_split.Initialize(true)) {
+    return -1;
+  }
+  return 0;
+}
+
+__BIONIC_WEAK_FOR_NATIVE_BRIDGE
+uint32_t __system_property_area_serial() {
+  prop_area* pa = __system_property_area__;
+  if (!pa) {
+    return -1;
+  }
+  // Make sure this read fulfilled before __system_property_serial
+  return atomic_load_explicit(pa->serial(), memory_order_acquire);
+}
+
+__BIONIC_WEAK_FOR_NATIVE_BRIDGE
+const prop_info* __system_property_find(const char* name) {
+  if (contexts == nullptr) {
+    return nullptr;
+  }
+
+  prop_area* pa = contexts->GetPropAreaForName(name);
+  if (!pa) {
+    async_safe_format_log(ANDROID_LOG_ERROR, "libc", "Access denied finding property \"%s\"", name);
+    return nullptr;
+  }
+
+  return pa->find(name);
+}
+
+static bool is_read_only(const char* name) {
+  return strncmp(name, "ro.", 3) == 0;
+}
+
+__BIONIC_WEAK_FOR_NATIVE_BRIDGE
+int __system_property_read(const prop_info* pi, char* name, char* value) {
+  while (true) {
+    uint32_t serial = __system_property_serial(pi);  // acquire semantics
+    size_t len = SERIAL_VALUE_LEN(serial);
+    memcpy(value, pi->value, len + 1);
+    // TODO: Fix the synchronization scheme here.
+    // There is no fully supported way to implement this kind
+    // of synchronization in C++11, since the memcpy races with
+    // updates to pi, and the data being accessed is not atomic.
+    // The following fence is unintuitive, but would be the
+    // correct one if memcpy used memory_order_relaxed atomic accesses.
+    // In practice it seems unlikely that the generated code would
+    // would be any different, so this should be OK.
+    atomic_thread_fence(memory_order_acquire);
+    if (serial == load_const_atomic(&(pi->serial), memory_order_relaxed)) {
+      if (name != nullptr) {
+        size_t namelen = strlcpy(name, pi->name, PROP_NAME_MAX);
+        if (namelen >= PROP_NAME_MAX) {
+          async_safe_format_log(ANDROID_LOG_ERROR, "libc",
+                                "The property name length for \"%s\" is >= %d;"
+                                " please use __system_property_read_callback"
+                                " to read this property. (the name is truncated to \"%s\")",
+                                pi->name, PROP_NAME_MAX - 1, name);
+        }
+      }
+      if (is_read_only(pi->name) && pi->is_long()) {
+        async_safe_format_log(
+            ANDROID_LOG_ERROR, "libc",
+            "The property \"%s\" has a value with length %zu that is too large for"
+            " __system_property_get()/__system_property_read(); use"
+            " __system_property_read_callback() instead.",
+            pi->name, strlen(pi->long_value()));
+      }
+      return len;
+    }
+  }
+}
+
+__BIONIC_WEAK_FOR_NATIVE_BRIDGE
+void __system_property_read_callback(const prop_info* pi,
+                                     void (*callback)(void* cookie, const char* name,
+                                                      const char* value, uint32_t serial),
+                                     void* cookie) {
+  // Read only properties don't need to copy the value to a temporary buffer, since it can never
+  // change.
+  if (is_read_only(pi->name)) {
+    uint32_t serial = __system_property_serial(pi);
+    if (pi->is_long()) {
+      callback(cookie, pi->name, pi->long_value(), serial);
+    } else {
+      callback(cookie, pi->name, pi->value, serial);
+    }
+    return;
+  }
+
+  while (true) {
+    uint32_t serial = __system_property_serial(pi);  // acquire semantics
+    size_t len = SERIAL_VALUE_LEN(serial);
+    char value_buf[len + 1];
+
+    memcpy(value_buf, pi->value, len);
+    value_buf[len] = '\0';
+
+    // TODO: see todo in __system_property_read function
+    atomic_thread_fence(memory_order_acquire);
+    if (serial == load_const_atomic(&(pi->serial), memory_order_relaxed)) {
+      callback(cookie, pi->name, value_buf, serial);
+      return;
+    }
+  }
+}
+
+__BIONIC_WEAK_FOR_NATIVE_BRIDGE
+int __system_property_get(const char* name, char* value) {
+  const prop_info* pi = __system_property_find(name);
+
+  if (pi != 0) {
+    return __system_property_read(pi, nullptr, value);
+  } else {
+    value[0] = 0;
+    return 0;
+  }
+}
+
+static constexpr uint32_t kProtocolVersion1 = 1;
+static constexpr uint32_t kProtocolVersion2 = 2;  // current
+
+static atomic_uint_least32_t g_propservice_protocol_version = 0;
+
+static void detect_protocol_version() {
+  char value[PROP_VALUE_MAX];
+  if (__system_property_get(kServiceVersionPropertyName, value) == 0) {
+    g_propservice_protocol_version = kProtocolVersion1;
+    async_safe_format_log(ANDROID_LOG_WARN, "libc",
+                          "Using old property service protocol (\"%s\" is not set)",
+                          kServiceVersionPropertyName);
+  } else {
+    uint32_t version = static_cast<uint32_t>(atoll(value));
+    if (version >= kProtocolVersion2) {
+      g_propservice_protocol_version = kProtocolVersion2;
+    } else {
+      async_safe_format_log(ANDROID_LOG_WARN, "libc",
+                            "Using old property service protocol (\"%s\"=\"%s\")",
+                            kServiceVersionPropertyName, value);
+      g_propservice_protocol_version = kProtocolVersion1;
+    }
+  }
+}
+
+__BIONIC_WEAK_FOR_NATIVE_BRIDGE
+int __system_property_set(const char* key, const char* value) {
+  if (key == nullptr) return -1;
+  if (value == nullptr) value = "";
+
+  if (g_propservice_protocol_version == 0) {
+    detect_protocol_version();
+  }
+
+  if (g_propservice_protocol_version == kProtocolVersion1) {
+    // Old protocol does not support long names or values
+    if (strlen(key) >= PROP_NAME_MAX) return -1;
+    if (strlen(value) >= PROP_VALUE_MAX) return -1;
+
+    prop_msg msg;
+    memset(&msg, 0, sizeof msg);
+    msg.cmd = PROP_MSG_SETPROP;
+    strlcpy(msg.name, key, sizeof msg.name);
+    strlcpy(msg.value, value, sizeof msg.value);
+
+    return send_prop_msg(&msg);
+  } else {
+    // New protocol only allows long values for ro. properties only.
+    if (strlen(value) >= PROP_VALUE_MAX && !is_read_only(key)) return -1;
+    // Use proper protocol
+    PropertyServiceConnection connection;
+    if (!connection.IsValid()) {
+      errno = connection.GetLastError();
+      async_safe_format_log(
+          ANDROID_LOG_WARN, "libc",
+          "Unable to set property \"%s\" to \"%s\": connection failed; errno=%d (%s)", key, value,
+          errno, strerror(errno));
+      return -1;
+    }
+
+    SocketWriter writer(&connection);
+    if (!writer.WriteUint32(PROP_MSG_SETPROP2).WriteString(key).WriteString(value).Send()) {
+      errno = connection.GetLastError();
+      async_safe_format_log(ANDROID_LOG_WARN, "libc",
+                            "Unable to set property \"%s\" to \"%s\": write failed; errno=%d (%s)",
+                            key, value, errno, strerror(errno));
+      return -1;
+    }
+
+    int result = -1;
+    if (!connection.RecvInt32(&result)) {
+      errno = connection.GetLastError();
+      async_safe_format_log(ANDROID_LOG_WARN, "libc",
+                            "Unable to set property \"%s\" to \"%s\": recv failed; errno=%d (%s)",
+                            key, value, errno, strerror(errno));
+      return -1;
+    }
+
+    if (result != PROP_SUCCESS) {
+      async_safe_format_log(ANDROID_LOG_WARN, "libc",
+                            "Unable to set property \"%s\" to \"%s\": error code: 0x%x", key, value,
+                            result);
+      return -1;
+    }
+
+    return 0;
+  }
+}
+
+__BIONIC_WEAK_FOR_NATIVE_BRIDGE
+int __system_property_update(prop_info* pi, const char* value, unsigned int len) {
+  if (len >= PROP_VALUE_MAX) {
+    return -1;
+  }
+
+  prop_area* pa = __system_property_area__;
+
+  if (!pa) {
+    return -1;
+  }
+
+  uint32_t serial = atomic_load_explicit(&pi->serial, memory_order_relaxed);
+  serial |= 1;
+  atomic_store_explicit(&pi->serial, serial, memory_order_relaxed);
+  // The memcpy call here also races.  Again pretend it
+  // used memory_order_relaxed atomics, and use the analogous
+  // counterintuitive fence.
+  atomic_thread_fence(memory_order_release);
+  strlcpy(pi->value, value, len + 1);
+
+  atomic_store_explicit(&pi->serial, (len << 24) | ((serial + 1) & 0xffffff), memory_order_release);
+  __futex_wake(&pi->serial, INT32_MAX);
+
+  atomic_store_explicit(pa->serial(), atomic_load_explicit(pa->serial(), memory_order_relaxed) + 1,
+                        memory_order_release);
+  __futex_wake(pa->serial(), INT32_MAX);
+
+  return 0;
+}
+
+__BIONIC_WEAK_FOR_NATIVE_BRIDGE
+int __system_property_add(const char* name, unsigned int namelen, const char* value,
+                          unsigned int valuelen) {
+  if (valuelen >= PROP_VALUE_MAX && !is_read_only(name)) {
+    return -1;
+  }
+
+  if (namelen < 1) {
+    return -1;
+  }
+
+  if (__system_property_area__ == nullptr || contexts == nullptr) {
+    return -1;
+  }
+
+  prop_area* pa = contexts->GetPropAreaForName(name);
+
+  if (!pa) {
+    async_safe_format_log(ANDROID_LOG_ERROR, "libc", "Access denied adding property \"%s\"", name);
+    return -1;
+  }
+
+  bool ret = pa->add(name, namelen, value, valuelen);
+  if (!ret) {
+    return -1;
+  }
+
+  // There is only a single mutator, but we want to make sure that
+  // updates are visible to a reader waiting for the update.
+  atomic_store_explicit(
+      __system_property_area__->serial(),
+      atomic_load_explicit(__system_property_area__->serial(), memory_order_relaxed) + 1,
+      memory_order_release);
+  __futex_wake(__system_property_area__->serial(), INT32_MAX);
+  return 0;
+}
+
+// Wait for non-locked serial, and retrieve it with acquire semantics.
+__BIONIC_WEAK_FOR_NATIVE_BRIDGE
+uint32_t __system_property_serial(const prop_info* pi) {
+  uint32_t serial = load_const_atomic(&pi->serial, memory_order_acquire);
+  while (SERIAL_DIRTY(serial)) {
+    __futex_wait(const_cast<_Atomic(uint_least32_t)*>(&pi->serial), serial, nullptr);
+    serial = load_const_atomic(&pi->serial, memory_order_acquire);
+  }
+  return serial;
+}
+
+__BIONIC_WEAK_FOR_NATIVE_BRIDGE
+uint32_t __system_property_wait_any(uint32_t old_serial) {
+  uint32_t new_serial;
+  __system_property_wait(nullptr, old_serial, &new_serial, nullptr);
+  return new_serial;
+}
+
+__BIONIC_WEAK_FOR_NATIVE_BRIDGE
+bool __system_property_wait(const prop_info* pi, uint32_t old_serial, uint32_t* new_serial_ptr,
+                            const timespec* relative_timeout) {
+  // Are we waiting on the global serial or a specific serial?
+  atomic_uint_least32_t* serial_ptr;
+  if (pi == nullptr) {
+    if (__system_property_area__ == nullptr) return -1;
+    serial_ptr = __system_property_area__->serial();
+  } else {
+    serial_ptr = const_cast<atomic_uint_least32_t*>(&pi->serial);
+  }
+
+  uint32_t new_serial;
+  do {
+    int rc;
+    if ((rc = __futex_wait(serial_ptr, old_serial, relative_timeout)) != 0 && rc == -ETIMEDOUT) {
+      return false;
+    }
+    new_serial = load_const_atomic(serial_ptr, memory_order_acquire);
+  } while (new_serial == old_serial);
+
+  *new_serial_ptr = new_serial;
+  return true;
+}
+
+__BIONIC_WEAK_FOR_NATIVE_BRIDGE
+const prop_info* __system_property_find_nth(unsigned n) {
+  struct find_nth {
+    const uint32_t sought;
+    uint32_t current;
+    const prop_info* result;
+
+    explicit find_nth(uint32_t n) : sought(n), current(0), result(nullptr) {
+    }
+    static void fn(const prop_info* pi, void* ptr) {
+      find_nth* self = reinterpret_cast<find_nth*>(ptr);
+      if (self->current++ == self->sought) self->result = pi;
+    }
+  } state(n);
+  __system_property_foreach(find_nth::fn, &state);
+  return state.result;
+}
+
+__BIONIC_WEAK_FOR_NATIVE_BRIDGE
+int __system_property_foreach(void (*propfn)(const prop_info* pi, void* cookie), void* cookie) {
+  if (contexts == nullptr) {
+    return -1;
+  }
+
+  contexts->ForEach(propfn, cookie);
+
+  return 0;
+}